I don’t have sources inside Microsoft (or outside Microsoft for that matter!), but I am going to make a bold (??) prediction here.

The final Windows Vista UI is going to change. Microsoft can continue to deny this as long as it wants (can), but the truth is that the UI in the CTPs is not what we are going to see in RTM. And I don’t mean some minor changes/updates to the UI here. They are going to give us a great new look.